#include <stdio.h>
#include <errno.h>
#include <stdlib.h>
#include <string.h>

#include <unistd.h>
#include <sys/mman.h>

#include <pthread.h>

#include <libkern/OSCacheControl.h>

int main (void) {
  char *start, *p;
  int x;

  start = (char*)mmap(0, getpagesize(),
                      PROT_READ | PROT_WRITE | PROT_EXEC,
                      MAP_ANON | MAP_PRIVATE | MAP_JIT,
                      0, 0);

  if (start == (char*)-1) {
    perror("mmap");
    exit(1);
  }

#ifdef PTHREAD_JIT_WRITE_ALLOW_CALLBACKS_NP
  pthread_jit_write_protect_np(0);
#endif

  p = start;

#define W(type, x) do{ *(type*)(p) = (x); p += sizeof(type); }while(0)

#if defined(__amd64)
  W(uint8_t, 0xB8);             /* mov eax, ... */
  W(uint32_t, 42);
  W(uint8_t, 0xC3);             /* ret */

#elif defined(__arm64)
  W(uint32_t, 0x52800540);      /* mov w0, #0x2a */
  W(uint32_t, 0xd65f03c0);      /* ret */

#else
  #error Funny CPU that you have there
#endif

#ifdef PTHREAD_JIT_WRITE_ALLOW_CALLBACKS_NP
  pthread_jit_write_protect_np(1);
#endif

  // __builtin___clear_cache(p, p + 2 * sizeof(uint32_t));
  sys_icache_invalidate(start, p - start);

  x = ((int(*)(void))start)();
  printf("We got %d\n", x);

  return 0;
}